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... neg. cable is a bit loose connecting to battery. Will a low battery cause this lost communication thing?
Not sure exactly what you mean here. All battery cable connections must be corrosion-free & tight. Especially check the battery ground straps. A poor battery connection can cause the described symptoms. If no joy after cleaning & tightening all battery connections, I would consider taking it to a mechanic for a diagnosis. Then maybe you can DIY the repair.
 

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Which engine is in that vehicle?

If it's the 4cyl Ecotec, problem could be ground 105:


Service Information 2008 Pontiac G6 | G6 (VIN Z) Service Manual | Document ID: 2200174
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#PIC5003: No Crank / No CommWith U2105 U2106 U2108 U2109 (LE5 Only) - keywords 2.4 2.4L communication start - (Oct 15, 2008)


Subject: No Crank/No Comm with U2105 U2106 U2108 U2109 (LE5 Only)


Models: 2008-2009 Chevrolet Malibu

2006-2009 Pontiac G6

2009 Saturn Aura

This PI only applies to vehicles listed with (LE5) Engine only




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The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
A condition has been identified that could cause a NO crank/No communication on the LE5-4 cyl engine. This condition has been identified as a loose ground G105 behind the A/C compressor.

Recommendation/Instructions:
Remove the bolt from G105 and clean the engine block surface. You should also make sure the terminal is tight after the bolt is tightened up. There have been reported cases of the bolt bottoming out in the hole and not generating a clamp load on the terminal.

Important: Please reference Document ID: 1986240 for location purposes.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.



GM bulletins are intended for use by professional technicians, NOT a ""do-it-yourselfer"". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.
WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION


© 2012 General Motors Corporation. All rights reserved.
 

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This applies only if you have the onstar module:


Service Information 2008 Pontiac G6 | G6 (VIN Z) Service Manual | Document ID: 2324430
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#PIC4677C: No Start No Crank Intermittently / No Communication Over High Speed LAN - keywords connector inop inoperative lamp light loose message on onstar U0121 U0101 U2100 U1040 P0700 P2544 U0073 VCIM warning - (Aug 10, 2009)


Subject: No Start No Crank Intermittently/No communication over High Speed LAN


Models: 2008-2010 Chevrolet Malibu

2006-2010 Pontiac G6

2007-2010 Saturn AURA




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This PI was superseded to update model years. Please discard PIC4677B.


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The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
A customer may have a complaint of an intermittent no start, no crank condition, and or SES light on with I/P gauges intermittently inoperative while driving. Any of the following DTCs may be accompanied with this complaint. U0121, U0101, U2100, U104, P0700, P2544, U0073

Recommendation/Instructions:
Before beginning to deep dive into any diagnostics first (If equipped) check the VCIM module (Onstar) connector C3 (Black) to be sure that it has been fully seated. This connector has been increasingly showing up as the root cause for loss of HIGH speed LAN concerns.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.



GM bulletins are intended for use by professional technicians, NOT a ""do-it-yourselfer"". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.
WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION


© 2012 General Motors Corporation. All rights reserved.
 
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